Acoustic Ink Printers (AIP), utilize acoustic waves to drive ink droplets from an AIP Print head. Acoustic waves generate droplets that are smaller and more precisely directed then current ink jet printers. A description of AIP printers is provided in U.S. patent application Ser. No. 09/363,593 entitled Method and Apparatus to Provide Adjustable Excitement of a Transducer in a Printing System in Order to Compensate for Different Transducer Efficiencies, filed Jul. 29, 1999, assigned to Xerox Corporation and hereby incorporated by reference.
In order to provide oscillating energy for an AIP printhead, a RF source is typically coupled to the AIP printhead. Optimal transfer of power from the RF source to the AIP printhead occurs when the output impedance of the RF source matches the input impedance of a load. In an AIP system, the load is an AIP printhead. However, in typical AIP systems, several factors make it difficult to match the source and load impedance.
A first factor that makes it difficult to match impedances is the changing frequency output of the RF source. In AIP systems, the frequency of the RF source output continuously changes over a predetermined frequency range to prevent the formation of standing waves and resonant effects within the AIP printhead. Unfortunately, changing the frequency of the RF source also makes it difficult to create an impedance match between the RF source and the AIP printhead because the impedance of the AIP printhead is a function of frequency. Changing frequencies result in a varying reactive component of impedance that makes it difficult to maintain an impedance match.
A second complication that makes it difficult to create an impedance match arises from the changing number of ejectors being fired. A typical AIP printhead includes a plurality of ejectors distributed across the printhead. The number of ejectors fired changes with the density of ink needed on an image. For example, when printing a dark image, multiple ejectors may be fired simultaneously to darken a region of a drawing. When printing a xe2x80x9clightxe2x80x9d image, one or even no ejectors may be fired for extended periods of time. Each ejector is associated with an impedance. Thus, changing the number of ejectors fired changes the overall impedance of the printhead.
Due to the previously described difficulties, most current acoustic ink printing systems do not match impedances. Instead, current systems compensate for power losses by using higher powered RF sources that provide larger amounts of power. However, such systems are inefficient and consume significant amounts of power. The wasted power generates heat that must be removed.
Thus an improved method and apparatus to transfer power from a variable frequency source such as a RF source to a variable load such as an AIP printhead is needed.
An improved matching network for matching the impedance of a source of variable frequency oscillating energy to a variable load is described. The described matching network includes a first reactive element that adjusts a first capacitance according to the frequency of the received oscillating energy. The matching network also includes a second reactive element that adjusts a second capacitance according to the impedance of a load. By adjusting the impedances of the two reactive elements, an approximate impedance match between the variable frequency oscillating energy source and the variable load is achieved. The described matching network is particularly suitable for use in acoustic ink printing systems, although the matching network is also useful in other systems, and the invention should not be limited to acoustic ink printing systems.